This invention relates generally to radio frequency array antenna systems and more particularly to multi-beam array antenna systems adapted to form a plurality of simultaneously existing beams of energy, selected one or ones of such beams being associated with continuous wave (CW) radio frequency energy and selected one or ones of such beams being associated with pulsed radio frequency energy.
As is known in the art, an array antenna may be arranged so that it produces a plurality of simultaneously existing beams of radio frequency energy. One such antenna is described in U.S. Pat. No. 3,761,936, Multi-Beam Array Antenna, inventors Donald H. Archer, Robert P. Prickett and Curtis P. Hartwig, issued Sept. 25, 1973 and assigned to the same assignee as the present invention. As described therein, the array antenna is adapted to produce a plurality of simultaneously existing beams of radio frequency energy, each one of the beams having the gain and bandwidth of the entire aperture. Such array antenna has a wide application such as in a relay or transponder as described in U.S. Pat. No. 3,715,749, Multi-Beam Radio Frequency System, inventor Donald H. Archer, issued Feb. 6, 1973 and assigned to the same assignee as the present invention. As described therein, in one application a pair of multi-beam array antennas is used, one for reception and one for transmission. Radio frequency energy along a particular wavefront is focused to a particular output port of the array, detected, fed to a corresponding input port of the transmitting array and retransmitted back along the same direction as the received wavefront.
In many applications it is required that the transmitted radio frequency energy be either pulsed radio frequency energy, continuous wave (CW) radio frequency energy or both superimposed one on the other, i.e. pulse and CW energy simultaneously. Further, it is often desirable to transmit pulsed ratio frequency energy in one beam and continuous wave (CW) radio frequency energy in a different beam. Thus, for example, in response to the detection of a continuous wave energy signal it may be desired to transmit a pulsed radio frequency energy signal along the direction of the received signal or along some other direction; or alternatively, to transmit continuous wave radio frequency energy in response to the detection of pulsed radio frequency energy; and so forth.
One arrangement suggested to provide these features includes the use of a single beam forming network such as a radio frequency parallel-plate lens having output ports coupled to an array of antenna elements through radio frequency amplifiers, such as traveling wave tubes (TWT), and having input ports of the network coupled to a continuous wave (CW) radio frequency energy source. When it is desired to transmit pulse modulated radio frequency energy signals the desired modulation is applied to the relatively low power CW energy source feeding the input ports. The radio frequency amplifiers are powered full time to amplify the signals fed thereto. The arrangement requires that the radio frequency amplifiers operate full time, i.e. in a one hundred percent duty cycle, thereby requiring relatively large amounts of power and therefore a power supply having relatively large weight, volume and cost. Another suggestion is to pulse modulate the radio frequency amplifiers when pulse modulated energy is to be transmitted; however, such modulation effects, i.e. modulates, continuous wave energy which may be being transmitted in a different beam. These intermodulation effects, however, very often adversely distort the continuous wave energy signal being transmitted.